1. Field of Invention
The invention relates to a fuel reforming apparatus and to a method of controlling the fuel reforming apparatus and, more particularly, to a fuel reforming apparatus for reforming hydrocarbon fuel into hydrogen-rich fuel gas and to a method of controlling the fuel reforming apparatus.
2. Description of Related Art
Conventionally, as a fuel reforming apparatus of this type, there is proposed one that completely burns about half of hydrocarbon fuel and that subjects the other half to a partial oxidation reaction. For example, such a fuel reforming apparatus is disclosed in Japanese Patent Application Laid-Open No. 7-215702. In this apparatus, water vapors resulting from complete combustion and carbon monoxide resulting from the partial oxidation reaction are shifted to hydrogen and carbon dioxide through a shift reaction, whereby the yield of hydrogen is enhanced and production of soot is restrained. The “yield of hydrogen” means a ratio of an amount of hydrogen that has been produced actually to an amount of hydrogen that is to be obtained theoretically from raw materials in a chemical process.
However, such a fuel reforming apparatus has difficulty in restraining generation of soot completely. Even if hydrocarbon fuel is burnt completely under a stoichiometric air-fuel ratio, it is impossible to mix hydrocarbon fuel with air completely and cause complete combustion in the entire mixture, and it is difficult to always maintain a state of the precisely stoichiometric air-fuel ratio due to gauge errors resulting from supply of hydrocarbon fuel and air. Thus, a small amount of soot is generated because of the carbon in the hydrocarbon fuel.
In the above fuel reforming apparatus, generation of soot is restrained by supplying hydrocarbon fuel to be burnt completely with air of an amount slightly larger than an amount corresponding to the stoichiometric air-fuel ratio. However, even in this case, there is caused a problem of difficulty in obtaining a completely mixed state and realizing complete combustion in the entire mixture.